U.S. patent application number 12/971224 was filed with the patent office on 2012-06-21 for semiconductor structures having directly bonded diamond heat sinks and methods for making such structures.
This patent application is currently assigned to RAYTHEON COMPANY. Invention is credited to Mary K. Herndon, Ralph Korenstein, Chae Deok Lee.
Application Number | 20120153294 12/971224 |
Document ID | / |
Family ID | 46233208 |
Filed Date | 2012-06-21 |
United States Patent
Application |
20120153294 |
Kind Code |
A1 |
Korenstein; Ralph ; et
al. |
June 21, 2012 |
Semiconductor Structures Having Directly Bonded Diamond Heat Sinks
and Methods for Making Such Structures
Abstract
A semiconductor structure is bonded directly to a diamond
substrate by Van der Waal forces. The diamond substrate is formed
by polishing a surface of diamond to a first degree of smoothness;
forming a material, such as diamond, BeO, GaN, MgO, or SiO.sub.2 or
other oxides, over the polished surface to provide an intermediate
structure; and re-polishing the material formed on the intermediate
structure to a second degree of smoothness smoother than the first
degree of smoothness. The diamond is bonded to the semiconductor
structure, such as GaN, by providing a structure having bottom
surfaces of a semiconductor on an underlying material; forming
grooves through the semiconductor and into the underlying material;
separating semiconductor along the grooves into a plurality of
separate semiconductor structures; removing the separated
semiconductor structures from the underlying material; and
contacting the bottom surface of at least one of the separated
semiconductor structures to the diamond substrate.
Inventors: |
Korenstein; Ralph;
(Framingham, MA) ; Herndon; Mary K.; (Littleton,
MA) ; Lee; Chae Deok; (Acton, MA) |
Assignee: |
RAYTHEON COMPANY
Waltham
MA
|
Family ID: |
46233208 |
Appl. No.: |
12/971224 |
Filed: |
December 17, 2010 |
Current U.S.
Class: |
257/76 ;
257/E21.121; 257/E21.238; 257/E29.089; 438/462; 438/479 |
Current CPC
Class: |
H01L 23/3732 20130101;
H01L 21/187 20130101; H01L 2924/00 20130101; H01L 21/02488
20130101; H01L 21/0242 20130101; H01L 21/02458 20130101; H01L
21/0254 20130101; H01L 2924/0002 20130101; H01L 29/2003 20130101;
H01L 21/02502 20130101; H01L 2924/0002 20130101 |
Class at
Publication: |
257/76 ; 438/479;
438/462; 257/E29.089; 257/E21.121; 257/E21.238 |
International
Class: |
H01L 29/20 20060101
H01L029/20; H01L 21/304 20060101 H01L021/304; H01L 21/20 20060101
H01L021/20 |
Claims
1. A structure comprising: a layer of diamond having a surface with
peaks and valleys; and a second material disposed only in the
valleys to provide the structure with a surface having: the peaks
of the diamond layer; and, surface portions of the second material
disposed in the valley.
2. The structure recited in claim 1 including a second layer of
semiconductor material bonded directly to the surface of the
structure.
3. The structure recited in claim 1 wherein the major portion of
the surface of the structure is diamond.
4. The structure recited in claim 3 wherein at least 80 percent of
the surface of the structure is diamond.
5. The structure recited in claim 1 wherein the second material is
diamond.
6. The structure recited in claim 1 including a second layer of
semiconductor material bonded directly to the surface of the
structure by Van der Waal forces.
7. The structure recited in claim 1 wherein the second material is
a solid material.
8. A structure comprising: a layer of diamond and a second layer of
semiconductor material bonded directly to the surface of the
diamond.
9. The structure recited in claim 8 wherein the semiconductor
material is GaN.
10. A method for forming a structure, such method comprising:
polishing a surface of diamond to a first degree of smoothness;
forming a material over the polished surface to provide an
intermediate structure; re-polishing the material formed on the
intermediate structure to a second degree of smoothness smoother
than the first degree of smoothness.
11. The method recited in claim 10 wherein the formed material is
diamond.
12. The method recited in claim 10 wherein the formed material is a
thermally conductive oxide.
13. The method recited in claim 10 wherein the formed material is
BeO, GaN, MgO, or SiO.sub.2.
14. A method for bonding a semiconductor to a heat sink,
comprising: providing a structure comprising a semiconductor layer
having a bottom surface disposed on an underlying material; forming
grooves through the semiconductor layer and into the underlying
material; separating the semiconductor layer along the grooves into
a plurality of separate semiconductor structures; removing the
separated semiconductor structures from the underlying material;
and contacting the bottom surface of at least one of the separated
semiconductor structures to a heat sink.
15. The method recited in claim 14 wherein the semiconductor
structures are GaN structures.
16. The method recited in claim 14 wherein the heat sink is
diamond.
17. The method recited in claim 14 wherein the heat sink is
diamond.
18. The method recited in claim 17 wherein the contacting is
performed under a liquid.
19. The method recited in claim 18 wherein the liquid is a volatile
liquid.
20. The method recited in claim 19 wherein the liquid is water.
21. The method recited in claim 17 wherein the liquid evaporates
after the contacting.
22. The method recited in claim 15 wherein the semiconductor
structure is bonded to the diamond by Van der Waal forces.
23. A method for bonding a semiconductor to a diamond substrate,
comprising: providing a structure comprising a GaN epitaxial layer
having a bottom surface disposed on an underlying layer; forming
grooves through the GaN and into the underlying layer; applying a
chemical etchant to the grooves to separate the GaN into a
plurality of separate structures; removing the separated GaN
structures from the underlying layer; and contacting the bottom
surface of at least one of the separated GaN structures to the
diamond substrate.
24. The method recited in claim 23 wherein the bottom surface of at
the least one of the separated GaN structures to bonded to the
diamond substrate by Van der Waal forces.
25. The method recited in claim 24 wherein the diamond substrate is
formed by a method comprising: polishing a surface of diamond to a
first degree of smoothness; forming a material over the polished
surface to provide an intermediate structure; re-polishing the
material formed on the intermediate structure to a second degree of
smoothness smoother than the first degree of smoothness.
26. The method recited in claim 25 wherein the formed material is
diamond.
27. The method recited in claim 25 wherein the formed material is a
thermally conductive oxide.
28. The method recited in claim 25 wherein the formed material is
BeO, GaN, MgO, or SiO.sub.2
Description
TECHNICAL FIELD
[0001] This disclosure relates generally to semiconductors
structures having directly bonded diamond heat sinks and methods
for making such structures.
BACKGROUND
[0002] As is known in the art, diamond has been used as a heat
spreader to remove the heat generated by high power semiconductor
devices. Usually the diamond is bonded to the semiconductor chip
via a metal solder or other adhesive. The semiconductor junction,
where most of the heat is generated, is typically located a fair
distance away from the diamond heat spreader and thus heat removal
is not efficient. More particularly, processes have been developed
for bonding GaN to diamond; however an interlayer is used between
the GaN and the diamond. The interlayer is another thermal barrier
that limits the ability of the diamond to effectively conduct heat
away from the GaN epilayer. For example, in one method, a thin Si
layer (.about.10-20 .mu.m thick) is used as the interlayer and in
another process an oxide "glue" layer .about.10000 .ANG. is used as
the interlayer.
SUMMARY
[0003] In accordance with the disclosure, a semiconductor body is
bonded directly to a diamond substrate. With such structure, heat
removal from the semiconductor structure GaN is substantially
improved.
[0004] In one embodiment the semiconductor body comprises a GaN
epitaxial layer and wherein the epitaxial layer is directly bonded
to the diamond substrate.
[0005] In one embodiment, a structure is provided comprising: a
layer of diamond having a surface with peaks and valleys; and a
second material disposed only in the valleys to provide the
structure with a surface having: the peaks of the diamond layer;
and, surface portions of the second material disposed in the
valley.
[0006] In one embodiment, a second layer of semiconductor material
bonded directly to the surface of the aforementioned structure.
[0007] In one embodiment, the major portion of the surface of the
aforementioned structure is diamond.
[0008] In one embodiment, at least 80 percent of the surface of the
aforementioned structure is diamond.
[0009] In one embodiment, the second material is diamond.
[0010] In one embodiment, the aforementioned second layer of
semiconductor material is bonded directly to the surface of the
structure by Van der Wall forces.
[0011] In one embodiment, the second material is a solid
material.
[0012] In one embodiment, a structure is provided comprising: a
layer of diamond and a second layer of semiconductor material
bonded directly to the surface of the diamond.
[0013] In one embodiment, the semiconductor material is GaN.
[0014] In accordance with the disclosure, the GaN epitaxial layer
is directly bonded to the diamond heat conductor using only Van De
Waals forces which results in more efficient heat conduction away
from the junction and improved heat dissipation.
[0015] In one embodiment, a method is provided for forming a
structure, such method comprising: polishing a surface of diamond
to a first degree of smoothness; forming a material over the
polished surface to provide an intermediate structure; re-polishing
the material formed on the intermediate structure to a second
degree of smoothness smoother than the first degree of
smoothness.
[0016] In one embodiment, the formed material is diamond.
[0017] In one embodiment, the formed material is a thermally
conductive oxide.
[0018] In one embodiment, the formed material is BeO, GaN, MgO, or
SiO.sub.2.
[0019] In one embodiment, a method a method is provided for bonding
a semiconductor to a heat sink, comprising: providing a structure
comprising: a semiconductor layer having a bottom surface disposed
on an underlying material; forming grooves through the
semiconductor layer and into the underlying material; separating
the semiconductor layer along the grooves into a plurality of
separate semiconductor structures; removing the separated
semiconductor structures from the underlying material; and
contacting the bottom surface of at least one of the separated
semiconductor structures to a heat sink.
[0020] In one embodiment, the semiconductor structures are GaN
structures.
[0021] In one embodiment, the heat sink is diamond.
[0022] In one embodiment, the contacting is performed under a
liquid.
[0023] In one embodiment the liquid is a volatile liquid.
[0024] In one embodiment the liquid is water.
[0025] In one embodiment the liquid evaporated after the
contacting.
In on embodiment, the semiconductor structure is bonded to the
diamond by Van der Waals forces.
[0026] In one embodiment, a method is provided for bonding a
semiconductor to a diamond substrate, comprising: providing a
structure comprising a GaN epitaxial layer having a bottom surface
disposed on an underlying layer; forming grooves through the GaN
and into the underlying layer; separating the GaN along the grooves
into a plurality of separate structures; removing the separated GaN
structures from the underlying layer; and contacting the bottom
surface of at least one of the separated GaN structures to a
diamond substrate.
[0027] Thus, with such disclosure, a semiconductor surface is
bonded directly to diamond without the use of any adhesives or
interlayer. Further, contacting between the GaN and diamond surface
under water facilitates the formation of strong Van der Waals
bonding.
[0028] The details of one or more embodiments of the disclosure are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the disclosure will be
apparent from the description and drawings, and from the
claims.
DESCRIPTION OF DRAWINGS
[0029] FIG. 1 is a diagram showing steps in a process used to form
a diamond substrate in accordance with the disclosure;
[0030] FIGS. 1A-1C are sketches of the diamond substrate at various
stags in the fabrication thereof;
[0031] FIG. 2 is a diagram showing steps in a process used to bond
a semiconductor directly to the diamond substrate formed in
accordance with the process steps of FIG. 1 in accordance with the
disclosure; and
[0032] FIG. 3 is a sketch of the diamond substrate directly bonded
to the semiconductor.
[0033] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0034] Referring now to FIG. 1, a process is shown for forming a
diamond heat sink. First, a first diamond body 10 (FIG. 1A) is
formed using, for example, any conventional plasma deposition
process. The upper surface of the first diamond body 10 is polished
using a conventional diamond suspension process, here polished to a
degree of smoothness in the order of an Ra of between approximately
50-60 Angstroms. It is noted that even after the polishing, the
upper surface of the body has peaks 12 and valleys 14.
[0035] Next, material 16 (FIG. 1B), here for example, additional
diamond is grown on the polished diamond using the same plasma
deposition process used to form the first diamond body 10, thereby
forming a second diamond body 18. More particularly, the additional
diamond is formed by re-nucleation. This is performed by bias
enhanced nucleation (BEN). Thus, the process does not merely grow
more diamond on top of the structure 12 but rather takes advantage
of diamond re-nucleation to allow additional diamond to grow
everywhere on the polished diamond surface including inside voids
and crevices.
[0036] Next, the upper surface of the body 18 (FIG. 1B) is
re-polished to a second degree of smoothness (here for example, to
an Ra of approximately 20 Angstroms) smoother than the first degree
of smoothness to form body 19 (FIG. 1C). The resulting surface is
an optically polished surface. It is noted that the additional
material 16 may be, for example, BeO, GaN, MgO, or SiO.sub.2 or
other oxides with reasonable thermal conductivity. Thus, the
structure 19 comprises a layer of diamond 10 having a surface with
peaks 12 and valleys 14 and the second material 16 disposed only in
the valleys 14 to provide the structure 19 with a surface having:
the peaks 12 of the diamond layer 10 and, surface portions of the
second material 16 disposed in the valleys 14. Here, at least 80
percent of the surface is the peaks 12.
[0037] Next, referring to FIG. 2, a process is shown for directly
bonding a semiconductor to the optically polished upper surface of
the body 19 by Van der Waals forces. First, a composite substrate
20 is provided having a lower layer 22 of sapphire, a 2.5
micrometers thick layer 24 of GaN on the sapphire 22, a (Mg,Ca)O
layer 26, here 0.3 to 0.5 micrometers thick, and a second, upper,
epitaxially formed (1 to 5 micrometers thick) layer 28 of GaN on
the (Mg,Ca) O layer 26. The substrate 20 may be purchased from the
University of Florida, Gainesville, Fla., see a paper entitled
"Improved oxide passivation of AlGaN/GaN high mobility transistors"
by Gila et al. Applied Physics Letters 87, 1635303 (2005).
[0038] More particularly, a handle wafer, not shown, which could be
Silicon or glass, is bonded with glue to the top of the GaN layer
28. Next, grooves 30 are mechanically cut with a saw blade through
the semiconductor layer 28 and through layer 26 into layer 24, as
shown. Next, a dilute (10%) phosphoric acid solution is used to
separate the semiconductor layer 28 into a plurality of separate
semiconductor structures 32. More particularly, the etch undercuts
under the lower surface of the epitaxial layer 28 and along the
interface between the epitaxial layer 28 and the (Mg,Ca)O layer 26
thereby separating (i.e., removing) the separated semiconductor
structures 32 from the underlying material, i.e., layer 26. Here,
the separated structures 32 are small squares .about.2 mm.times.2
mm to facilitate (i.e., reduce the etching time) in the
undercutting by the phosphoric acid--otherwise it would take a very
long time for the acid to work its way through large areas.
[0039] Next, the bottom surfaces of the separated semiconductor
structures 32 are contacted to the smoothed upper surface of the
diamond structure 19 formed in accordance with the process
described above in connection with FIG. 1. It is noted that the
bottom surface of the structures 32 and the upper surface of
structured 18 are brought together under water. Alternatively, a
few water droplets are placed between the surfaces to be bonded.
Next, the handle is then removed after attachment to diamond is
complete. Any remaining water being evaporated resulting in a bond
process wherein Van der Waals attractive forces are developed
between optically contacted (i.e., extremely smooth) surfaces. The
resulting bonded structure is shown in FIG. 3. Once the bonding
steps are completed the handle wafer is removed from the top of the
GaN layer 28 by means of organic solvents.
[0040] A number of embodiments of the disclosure have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the disclosure. Accordingly, other embodiments are within
the scope of the following claims.
* * * * *